Soft matter nanoparticles based on polyglycerols as efficient multimodal imaging agents for EGF-receptor tumor targeting

Nano-constructs based on macromolecules have become increasingly interesting in the recent years owing to their unique properties like high aqueous stability, biocompatibility etc. in the field of drug delivery, nanomedicine as well as for multi modal imaging. Having multiple modalities on a single carrier molecule obviate the need to administer several compounds with different pharmacokinetics. In this regard, dendritic polyglycerols (dPG) are globular macromolecules with a nano-size (5-20 nm), narrow size distribution (PDI >1.26), high degree of branching and high end group functionalities which makes them amenable to a wide range of chemical modifications.[1] This great versatility allows dendritic polyglycerols to be fine-tuned with respect to various physico-chemical parameters such as particle size, water solubility, surface charge, chemical functionalities, etc, that are relevant for the successful preparation of theranostic systems. Previous studies done on 3H and 64Cu radiolabeled anionic and neutral dPG shows their great potential as platforms for various applications.[2] The presented work here deals with the development of a dendritic polyglycerol derivative as a dual-modal agent for epidermal growth factor receptor (EGFR) specific tumor targeting. In this respect, in a one pot reaction, simultaneously maleimido- bearing fluorescent labels (dye) for in vitro or vivo imaging (cy3/cy7) and macrocyclic chelators for 64Cu (PET tracer) were attached to thiol anchoring groups of the polymeric scaffold. For an EGFR specific targeting, a small camelid single-domain antibody (sdAb) representing a potential recognition agent for EGFR was attached via a PEG linker. For a controlled purification, an affinity chromatography procedure was used which selectively separates the antibody conjugated multimodal conjugates. This leads to a higher affinity and selectivity of the dual modal conjugates on the tumor cells. 64Cu radiolabeling was done under ambient temperature and physiological pH. Binding and uptake studies were performed using A431 and FaDu cell lines using 64Cu-labeled bioconjugates. Confocal laser scanning microscopy was used to study the receptor-mediated cellular uptake as well as scavenger receptor studies which show a selective affinity of dPG conjugates to the tumor cells. Antibody-dPG multimodal conjugates were injected intravenously to mouse xenografted models for in vivo studies using PET imaging as well as optical imaging which reveal a good tumor targeting of the conjugates. These results reveal an excellent potential of dendritic polyglycerols as multimodal platforms for various biomedical applications.